Fine particles are classified into particles of a diameter larger than 100 nm and particles of a diameter smaller than 100 nm that are so-called ultrafine particles. The particles larger than 100 nm have been used from old times as constituent materials of cement, cosmetics, toner for electronic copying, and the like, whereas the particles smaller than 100 nm are used in materials field of ceramics, magnetic tape, super LSI element and the like. As the method for producing such ultrafine particles, a metal alkoxide hydrolysis method, a coprecipitation method, an inorganic salt hydrolysis method, a spray-drying method, a plasma method, a laser method and the like are known, and it is possible to obtain ultrafine particles of a nanometer order. For example, nanosized fine silica particles smaller than 100 nm, which are known as a silica sol or a colloidal silica, are produced by a method of neutralizing sodium silicate with an acid or a method of hydrolyzing a tetraalkoxysilane followed by condensation polymerization (see nonpatent literatures 1 and 2). This colloidal silica is sphere-shaped, and is a spherical colloid dispersed in a polar solvent such as water and an alcohol, and is already dispersing uniformly in a solvent. In addition, a method of synthesizing a mesoporous silica having a nanosized porous structure by hydrolyzing a tetraalkoxysilane in the presence of a cationic surfactant followed by condensation polymerization, is known (see nonpatent literature 3).
Although nanometer order ultrafine particles can be produced by such hydrolysis methods of an alkoxysilane, the particle diameter distribution of the obtained ultrafine particles is not uniform but usually broad. In addition, the shape of the particles is indeterminate form.
Consequently, a process for producing ultrafine silica particles having a uniform diameter, in which, using a dendrimer with silylated surface, the ultrafine silica particles are produced on the surface of a dendrimer, is proposed (see patent literature 1).
In addition, a method for improving heat resistance, mechanical characteristics, gas-barrier nature and the like of a resin, by inserting a quaternary ammonium salt or the like between the layers of a swelling phyllosilicate compound having a particle diameter of 0.1 to several ten μm and dispersing salt thereof in the resin, is studied (see patent literature 2). The development of a resin composite made of ultrafine particles having a further small particle diameter is demanded, and it is considered that, if nano-sized and plate-shaped fine silica particles could be produced, particles thereof can be used as a filler to be blended in various resins to improve the characteristics of the obtained composite material such as heat resistance, gas-barrier nature and a lower expansion coefficient while keeping dispersibility of the particles in the resins. Colloidal silica dispersed uniformly in a solvent already, therefore, is compounded with a resin by a seed polymerization method and the like while keeping the dispersion state (see patent literature 3). The composite material produced by such a method, however, has not satisfactory characteristics. In addition, for this reason, a solid powder of fine silica particles to be obtained by hydrolyzing a tetrafunctional hydrolyzable silane compound in water in the presence of a cation surfactant followed by condensation polymerization and discontinuing the reaction using a monofunctional hydrolyzable organosilane compound halfway in the reaction, has been developed (see patent literature 4). The above fine particles are a powder of plate-shaped fine silica particles that contains 10% or less of a component having a molecular weight of 1 million or more based on the area ratio of the differential molecular weight distribution curve measured in polystyrene equivalent by gel permeation chromatography and has a number-average molecular weight of 1,500 to 100,000 obtained in the above measurement, a maximum length less than 200 nm, an average length of 1 to 50 nm and at least a triorganosilyl group on the surface and these particles have film-forming nature and can form a thin film.
According to spread of a portable electronic device represented by a cellular phone and a laptop PC, a thin secondary battery having a high energy density is under development. A mesoporous silica having a structure where mesopores of a uniform diameter are arranged draws attention as an inorganic solid electrolyte for such a secondary battery. Such a mesoporous silica having a regular pore structure is known to show various macroscopic morphology, and can be subjected to diverse morphological control, and is expected to be applied for a functional material such as an optical material and an electronic material besides a conventional application such as a catalyst and an adsorbent. For example, a model of an ion channel is proposed, which is constructed by an aggregate of a surfactant formed in the pores of a mesoporous silica using the mesoporous silica, alkylpolyethylene oxide as the surfactant and lithium trifluorometane sulfonate as an electrolyte, and a lithium ion of the electrolyte transfers via the polyethylene oxide part of the aggregate. A new type of ion-conductive solid electrolyte free from faults of a conventional secondary battery has been developed by using such a mesoporous silica. For example, an ion-conductive solid electrolyte is proposed, which is produced by hydrolyzing a silicon compound in the presence of a substance having ion conductivity in the molecule such as a nonionic surfactant to form a mesoporous silica having a lamellar structure and then treating the obtained mesoporous silica in a magnetic field to provide orientation to the mesostructure in the electrolyte (see patent literature 5).
Such ultrafine silica particles having mesopores and a regular structure is greatly expected as a material for improving resin characteristics and a solid electrolyte for a secondary battery, besides as a conventional application such as a catalyst and an adsorbent. Development of an ultrafine silica as a nanotechnology material has drawn attention.    Patent Literature 1: JP-A-2003-2632    Patent Literature 2: JP-A-11-92677    Patent Literature 3: JP-A-9-194208    Patent Literature 4: JP-A-2005-2146    Patent Literature 5: JP-A-2002-42550    Nonpatent Literature 1: Ultrafine Particles—Science and Application—Edited by The Chemical Society of Japan, Kagaku Sousetu No. 48, Gakkai Shuppan Center (1985)    Nonpatent Literature 2: Simodaira, Ishijima: Bulletin of the Chemical Society of Japan, 1503-1505 (1981)    Nonpatent Literature 3: Langmuir Vol. 16, 2376 (2000)